The present invention relates to an improved thermosensitive recording material, and more particularly to a thermosensitive recording material comprising a support material and a thermosensitive coloring layer formed on the support material, which thermosensitive coloring layer comprises a colorless or light-colored coloring material and a developing material, which developing material contains p-hydroxybenzoic acid ester and a bisphenol derivative, and which colors the coloring material upon application of heat thereto.
Recently, thermosensitive recording materials have been employed in a variety of fields, for instance, for use with printers of computers, recorders of medical analytical instruments, facsimile apparatus, automatic ticket vending apparatus, and thermosensitive copying apparatus, since they have the following advantages over other recording materials:
(1) Images can be formed by simple heat application, without any complicated steps for development. PA1 (2) The thermosensitive recording materials can be produced by a simple apparatus and the storage of the thermosensitive recording materials is simple and does not involve excessive costs. PA1 (3) As the support material of the thermosensitive recording materials, paper is usually used, which is rather inexpensive in comparison with other support materials, such as synthetic resin films. PA1 (4) When paper is used as the support material, the thermosensitive recording material has a pleasing plain-paper-like touch. PA1 3,3-bis(p-diethylaminophenyl)-phthalide, PA1 3,3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide (or Crystal Violet Lactone), PA1 3,3-bis(p-dimethylaminophenyl)-6-diethylaminophthalide, PA1 3,3-bis(p-dimethylaminophenyl)-6-chlorophthalide, and PA1 3,3-bis(p-dibutylaminophenyl)-phthalide. PA1 3-cyclohexylamino-6-chlorofluoran, PA1 3-(N,N-diethylamino)-5-methyl-7-(N,N-dibenzylamino)fluoran, PA1 3-dimethylamino-5,7-dimethylfluoran, PA1 3-diethylamino-7-methylfluoran, and PA1 3-diethylamino-7,8-benzfluoran. PA1 3-diethylamino-6-methyl-7-chlorofluoran, PA1 3-pyrrolidino-6-methyl-7-anilinofluoran, PA1 2-[N-(3'-trifluoromethylphenyl)amino]-6-diethylaminofluoran, and PA1 2-[3,6-bis(diethylamino)-9-(o-chloroanilino) xanthylbenzoic acid lactam]. PA1 3-(2'-hydroxy-4'-dimethylaminophenyl)-3-(2'-methoxy-5'-chlorophenyl) phthalide, PA1 3-(2'-hydroxy-4'-dimethylaminophenyl)-3-(2'-methoxy-5'-nitrophenyl) phthalide, PA1 3-(2'-hydroxy-4'-diethylaminophenyl)-3-(2'-methoxy-5'-methylphenyl) phthalide, and PA1 3-(2'-methoxy-4'-dimethylaminophenyl)-3-(2'-hydroxy-4'-chloro-5'-methylphen yl) phthalide.
A conventional thermosensitive recording material is produced by coating on a support material (for instance, a sheet of paper or a synthetic resin film) a thermosensitive coloring liquid, containing a coloring material and a developing material, which can be colored when heated, and then by drying the coloring liquid to form a thermosensitive coloring layer.
Images are formed and recorded in the thus produced thermosensitive recording material by heat application by use of a thermal pen or head.
Thermosensitive recording materials of the above-described type are disclosed, for instance, in Japanese Patent Publications No. 43-4160 and No. 45-14039. Such thermosensitive recording materials, however, have the following shortcomings.
During the application of heat to the recording material for recording by a thermal pen or head, materials contained in the thermosensitive coloring layer are fused and adhere, in the form of particles, to the thermal pen or head. The particles then stick to the thermosensitive recording material itself and hinder the feeding thereof, or they are transferred back to the recording material, leaving trailing marks on the recording material.
Furthermore, when the sticky particles accumulate on the thermal pen or head, image density and image sharpness tend to decrease, and images are deformed.
These conventional thermal recording materials are also slow in thermal response, not allowing rapid recording with high image density and high image sharpness, and there is in fact a keen demand for rapid recording, for instance, in facsimile, and recorders for computers and medical analytical instruments. The thermal response of thermal recording materials is called their "head matching property" and is considered to be an important factor when evaluating the quality of thermal recording materials.
In Japanese Laid-open Patent Application No. 48-19231, there is disclosed a method of adding waxes with a melting point in the range of 40.degree. C. to 100.degree. C. to the thermosensitive coloring layer of a thermal recording material in an attempt to improve the thermal response.
In Japanese Patent Publication No. 51-27599, there is disclosed a method of adding a fatty acid amide and a petroleum wax to the thermosensitive coloring layer in an attempt to improving the thermal response and to reduce the adhering of sticky particles to the thermal head.
By these methods, however, the sticky particles, the adhesion thereof to the thermal head and the trailing marks formed on the thermosensitive recording material by the particles cannot be eliminated sufficiently for practical use and, accordingly, high image density and high image sharpness that are acceptable for practical use cannot be obtained.